The present invention relates to a drill string element adapted to be coupled to other similar drill string elements by thread connections thus forming a drill string for top hammer drilling. Each drill string element includes at least one rod for transferring impact energy to a drill bit provided at the lower end of the drill string and a tube assembly for transferring rotation to the drill bit, the tube assembly surrounding the rod. The invention also relates to a tubular member adapted to be included in a drill string element according to the invention.
Drill string elements of the above-mentioned type are previously known from U.S. Pat. No. 4,094,364. However, these drill string elements have the disadvantage that when they are separated from each other by unscrewing the thread connections in question the rod can fall out of the surrounding tube assembly in one direction. This is a considerable disadvantage in respect of handling, especially regarding workers' protection. However, the wanted characteristic of having the rod safely secured within the tube assembly must be combined with a necessary accessibility to the interior of the drill string element, e.g. in connection with service or repair. Also the tube assemblies must be kept intact at normal handling during operation.
The present invention has the aim of presenting a drill string element of the above-mentioned kind having a rod that is safely secured within the tube assembly and also having good accessibility in connection with service/repairs.